Self-equalizing, self-aligning body support



April 16, 1957 E. R. DYE ETAL 2,788,531

sELF-EQUALIZING, SELF-ALIGNING BODY SUPPORT Filed Dec. 30, 195s JNVENTORS BY M @W .4 7" TOD/VE' YS United States Patent O SELF-EQUALIZING, SELF-ALIGNING BODY SUPPDRT Edward R. Dye, Orchard Park, and Murray Kamrass, Buffalo, N. Y., assignors to Cornell Aeronautical Lab oratory, Inc., Buffalo, N. Y., a corporation of New York Application December 30, 1953, Serial No. 401,148

2 Claims. (Cl. 5-191) This invention relates to apparatus and method for supporting a human body when reclining.

When the human body is reclining, it should be supported so that the spinal column is in a straight line. Also, the body should be supported proportional to the distribution of weight. A further requirement for optimum support is to make the intensity of pressure as uniform as possible over the surface of the body. If these three requirements are met, a person should receive the most restful sleep.

These requirements are realized with the apparatus and method forming the subject of the present invention.

Secondary objects and advantages will be apparent from the following description and accompanying drawings in which:

Fig. l is a top plan view of a self-equalizing, self aligning cot suspension embodying the present invention.

Fig. 2 is a side elevational View thereof and illustrating the displacement of the suspension when a human body reclines on the cot and also showing a chart representing numbered imaginary stations along the length of the body.

Fig. 3 is an end elevational view `of the head end or right end of the cot shown in Fig. 2.

Fig. 4 is a diagram of elements and displacements of i the cot suspension at a typical crosssectiom Fig. 5 is a vector diagram of the forces involved in the right halfvof the diagrammatically represented suspension of Fig. 4. y

Fig. 6 is an enlarged fragmentary cross sectional view through the end of one of the transverse support members and showing the manner in which this end is mounted on the cot frame.

While the invention may be embodied in dilerent types of body supporting apparatus such as hospital equipment, stretchers and furniture, the invention is illustrated as being embodied in a cot.

The cot is `shown as having a frame comprising a pair of spaced parallel horizontal side frame members 10, 10 supported adjacent each end by a U-shaped member 11 with a similar U-shaped member 12 arranged intermediate the end members 11. These members 10, 11 `and 12 are preferably formed of round` metal tubes. The end mem- Ibers 11 are preferably set in from the ends of the side frame members 10 so as to leave handles 13. The upper ends of the legs of the U-shaped members 11 and 12 are suitably rigidly connected to the side frame members 10 and these legs are of the same height so that the side frame members 10 will be horizontal when the cot is set on a at horizontal surface such as a floor.

The suspension part of the cot comprises a multiplicity of transverse load carrying straps each represented by the numeral 14 and a series of longitudinal elastic strips 15.

Each of the transverse load carrying straps 14 includes a central non-elastic part 16and an elastic part 17 at each end thereof. While the elastic part 17 as a single reach may be` connected at one end to the adjacent end rice of its companion nonelastic part 16 and the opposite end to the adjacent side frame member 10, it is preferred to form each elastic part 17 into a loop passing around the frame member and fastened at its opposite ends to the end portion of the non-elastic part as best shown in Fig. 6. The method of fastening may be by stitching as shown and represented at 18.

The length of each composite transverse strap 14 is the same when unloaded but it will be observed by referring to Fig. l that the proportionate lengths of elastic and non-elastic parts in each such strap varies from one to another. The purpose for this will be later explained herein.

The transverse composite straps 14 are composed of the same width material and are uniformly spaced along the side frame members 10 and deflect varying amounts under load as shown in Fig. 2. In order to maintain the spacing of such transverse straps 14, the spaced longitudinal elastic strips 15 are shown as being passed alternately over and under the transverse straps and are fastened at their places of overlapping in any suitable manner as by stitching 19. These longitudinal elastic strips 15 act as ties and do not have any load carrying function.

To attain maximum body comfort on the cot, the suspension of the cot should deform to accommodate the local weight and dimensions of the body. In accordance with the present invention this is accomplished by varying the elasticity of the cot suspension along its length. As an approximation to the actual system, reference is made to Fig. 4 wherein a weight W is applied to the transverse composite strap which has a non-elastic central portion 16a and an elastic portion 17a at each end connected to the side frame bars 10a, 10a. The horizontal spacing between the side frame bars 10a remains constant and one half such spacing is considered as x. Therefore the tension in the composite strap is a function of the weight W and the deflection y.

It will now be shown that by specifying the values of W and y the characteristics of the spring or elastic portions at the ends of the straps can be determined. Fig. 5 is a vector diagram of the forces involved wherein F is the tension in the composite strap with the vertical component and the horizontal component. From relating the similar triangles shown in Figs. 4 and 5 and solving for F the following equation results:

Since the elastic will stretch in proportion to the tension in the strap; another equation can be written as follows:

3 Substituting #(3) into (2) and equating (2) to (l) elastic-material, it is/possible to vary k by varyingl the lengthv in accordance with the equation (6) K=kL wherein K is the modulus of the spring or elastic per unit length and L is the spring length. Solving for L, there results (7) E M a;

*1G-W am@ In the case ofrailo'adwhichis moreor less distri'butedrsuch as would be applied by parts ofv the body, the above analysis is not exact. Nevertheless, the general principles of design are applicable with theexception that the expression for L becomes more complex although it need not contain new variables.' For the practical` case yof designing a cot to support a human being, average-dimensions and weights can be assumed so that the cot will be suitable for most persons of reasonable proportions. It is tovbe noted that modifications ofi-the system can be devised for sitting and other positionsof reclining.

For the case wherethere is a nite spacing between adjacent transverse' straps 14 and where the elastic members 17 are Wrapped varound a tubular frame'member 10, as shown, Equation 7 must be multiplied by the factor 21S, where S is thel spacing between the centerlines of adjacent straps (see Fig. 2) and the factor of 2 is required to account for the looping or doubling ofthe elastic member 17 whose effective length is L (see Fig. 6). Thus the equation becomes Zan fc (8) L WS 1 am) in which:

L=elastic length in inches x=half the width of cot in inches K=modnlus ot' a one inch length of elastic y=deforrnation ot' strap due to body contour (in inches) W :local weight of body in pounds `Yper inch of height Szspacing between adjacent strap eenterlines in inches x=l5 inches K-:ZS pounds per inch .8:2 inches y=halt width of body (see table) W=local weight of body (see table) Then Equation Sireduces to The following values, for example, can be used The right hand column captioned L in the following table lists thecalculatednvalues ofmtheet`fective..lengthLninl inches for each elastic loop 17 shown in Fig. 6.

Station Y, inches W,1bs./in. L, inches From a practical point of view, a particular strap suspension. designedas illustrated above is equally effective whether the lhuman body is lying onthe back or-sideinas' much as the stretchof the spring'or elastic portions at each-station of the body'willbe approximately 'the-same', f

considering the contour of the body.

From the foregoing it will be seen-that the present inventionvprovides an apparatus andmethod for human body suspension which simultaneously provides for Ythel correct --weight support and the properdeformation-.for each transverse element of the-body so-that no'vertical shear force isy developed between the transverse elements andiat the same time having the longitudinal axis of the The transverse strap support body held in a straight line. mechanism of 'the present invention has an elastic link which'fromstrap tostrap varies in length-to adjust for vthe sag and weightrequired ofit. This is accomplished automatically by the apparatus requiring noV external adjustment. It is pointedlout furthery that in the apparatusrof 'the inventionthe transverse straps when unoccupied are not prestressed` or only'negligibly as aresult 0f the weight of the straps and this is uniform: By arranging'the nonlelastic part` of the transverse strap' in the centerbetween'V theelasti'c ends, the Vbody lcontacts' the non-elastic part and'doesnot interfere'with they stretching portions inv all straps being substantially non-prestressed,

and the ratioofrthe length Vofthe non-elasticportionto the`A- elastic portions in each `strap beingsuch that'the StrapstretChes-'to the necessary lengthtoprovide the deformation correspondingto theordinatefofithe section of the-body engaged thereby and rat-lthetsame time exerts atensionvwhich.; produces a1 vertical 4resistance substantiallyaequal tothe Weight of the section ofitheibodyz supported, the' length of each-elasticfportion'inteachtransverse strap being determined generally in accordance with the following equation in which:

L is the length of the elastic portion, in inches K is the modulus of a one inch length of the elastic portion W is the weight of the section of the body, in pounds x is half the spacing between the frame members, in inches y is the ordinate of strap displacement to accommodate the section of the body, in inches.

strap stretches to the necessary length to provide the de- 2 formation corresponding to the ordinate of the body engaged thereby and at the same time exerts tension which produces a vertical resistance substantially equal to the weight of the section of the body supported, the length of each elastic portion in each transversel strap being determined generally in accordance with the following equation 4 aq *HL) L WS l $24.312 in which:

L is the length of the elastic portion, in inches K is the modulus of a one inch length ofthe elastic portion W is the weight of the section of the body, in pounds S is the spacing between adjacent strap centerlines, in

inches x is half the spacing between the frame members, in

inches y is the ordinate of strap displacement to accommodate the section of the body, in inches.

References Cited in the file of this patent UNITED STATES PATENTS 34,971 Lambert Apr. 15, 1862 2,127,710 Baker Aug. 23, 1938 2,652,966 Griswold Sept. 22, 1953 FOREIGN PATENTS 31,519 Denmark Apr. 5, 1923 47,087 France Sept. 22, 1936 

